Stochastic communication protocol method and system for radio frequency identification (RFID) tags based on coalition formation, such as for tag-to-tag communication

ABSTRACT

Data carriers (such as RFID tags) are formed into clusters of data carriers. Each cluster has at least one bridge data carrier that can communicate with a bridge data carrier of another cluster, thereby allowing data carriers in each cluster to communicate directly or indirectly with each other using a stochastic communication protocol method. Direct tag-to-tag communication capability is provided between data carriers in each cluster and/or between clusters. The data carriers can backscatter and modulate a carrier wave from a source, thereby using the backscattered and modulated carrier wave to convey data to each other.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a national stage application of PatentCooperation Treaty (PCT) Application Ser. No. PCT/US2006/036801, filedSep. 21, 2006, which in turn claims priority to U.S. Provisional PatentApplication Ser. No. 60/719,102, entitled “STOCHASTIC COMMUNICATIONPROTOCOL AND METHOD OF COALITION FORMATION FOR RF ID TAGS,” filed Sep.21, 2005. These applications are assigned to the same assignee as thepresent application, and incorporated herein by reference in theirentireties.

TECHNICAL FIELD

This disclosure generally relates to the field of automatic datacollection (ADC), for example, data acquisition via radio frequencyidentification (RFID) tags and readers. More particularly but notexclusively, the present disclosure relates to communication betweendata carriers such as RFID tags.

BACKGROUND INFORMATION

The ADC field includes a variety of different types of ADC data carriersand ADC readers operable to read data encoded in such data carriers. Forexample, data may be encoded in machine-readable symbols, such asbarcode symbols, area or matrix code symbols, and/or stack code symbols.Machine-readable symbols readers may employ a scanner and/or imager tocapture the data encoded in the optical pattern of such machine-readablesymbols. Other types of data carriers and associated readers exist, forexample magnetic stripes, optical memory tags, and touch memories.

Other types of ADC carriers include RFID tags that may store data in awirelessly accessible memory, and may include a discrete power source(i.e., an active RFID tag), or may rely on power derived from aninterrogation signal (i.e., a passive RFID tag). RFID readers typicallyemit a radio frequency (RF) interrogation signal that causes the RFIDtag to respond with a return RF signal encoding the data stored in thememory.

Identification of an RFID tag generally depends on RF energy produced bya reader or interrogator arriving at the RFID tag and returning to thereader. Multiple protocols exist for use with RFID tags. These protocolsmay specify, among other things, particular frequency ranges, frequencychannels, modulation schemes, security schemes, and data formats.

Many ADC systems that use RFID tags employ an RFID reader incommunication with one or more host computing systems that act ascentral depositories to store and/or process and/or share data collectedby the RFID reader. In many applications, wireless communications isprovided between the RFID reader and the host computing system. Wirelesscommunications allow the RFID reader to be mobile, may lower the costassociated with installation of an ADC system, and permit flexibility inreorganizing a facility, for example a warehouse.

RFID tags typically include a semiconductor device having the memory,circuitry, and one or more conductive traces that form an antenna.Typically, RFID tags act as transponders, providing information storedin the memory in response to the RF interrogation signal received at theantenna from the reader or other interrogator. Some RFID tags includesecurity measures, such as passwords and/or encryption. Many RFID tagsalso permit information to be written or stored in the memory via an RFsignal.

RFID tags are generally used to provide information about the specificobjects on which the RFID tags are attached. For example, RFID tags maystore data that provide the identification and description of productsand goods, the identity of an animal or an individual, or otherinformation pertaining to the objects on which the RFID tags areattached.

Some types of RFID tags are capable of communicating with each other,thereby allowing formation of an RFID network. However, directtag-to-tag communication in such RFID networks is currently possibleonly between specially designed battery-powered active RFID tags, suchas the products available from Axcess Inc. and/or the devices used inthe “Smart Dust: Autonomous sensing and communication in a cubicmillimeter” project described inhttp://robotics.eecs.berkeley.edu/˜pister/SmartDust/. Such active RFIDtags and devices can be unduly complex in design and expensive,especially in situations requiring a large number of tags where thebatteries have to be continuously monitored, maintained, and replaced inorder to ensure that sufficient power is available to meet operationalrequirements.

Moreover, traditional client-server applications and methods are notparticularly suited for RFID networks that need to be capable ofhandling very large numbers of interconnected RFID tags in an ad hocmanner. In addition, the RFID tags may dynamically join or leave theRFID network due to a number of reasons, such as exhaustion or lost ofpower, signal attenuation, physical destruction, etc. The dynamic andgenerally random nature of the interconnection between and presence ofRFID tags, combined with a potentially massive number of distributedRFID tags, as a practical matter preclude the use of traditionalapplications and methods for communications.

As an additional consideration, the routing table approach used in wirednetworks and in wireless networks (such as 802.11, ZigBee, Bluetooth,etc. wireless systems) requires a relatively large amount of memory,which is not readily available in RFID tags and therefore cannot beconveniently used in RFID networks. Furthermore, the traditionalcommunication applications and methods are generally unsuitable in RFIDnetworks where the complexity of interconnections between RFID tagsrequires such communication applications/methods to address scalability,pervasiveness, spatial distribution, power awareness, and/or otherissues.

BRIEF SUMMARY

One aspect provides a method that includes forming coalitions ofclusters of distributed data carriers. For each of said clusters, themethod identifies a bridge data carrier that is capable to link with abridge data carrier of another of said clusters, and enablescommunication between data carriers of the clusters. At least some ofsaid data carriers include batteryless passive data carriers.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments are described with referenceto the following drawings, wherein like reference numerals refer to likeparts throughout the various views unless otherwise specified. The sizesand relative positions of elements in the drawings are not necessarilydrawn to scale. For example, the shapes of various elements and anglesare not drawn to scale, and some of these elements are arbitrarilyenlarged and positioned to improve drawing legibility. Further, theparticular shapes of the elements as drawn, are not intended to conveyany information regarding the actual shape of the particular elements,and have been solely selected for ease of recognition in the drawings.

FIG. 1 is a schematic diagram showing a formation of clusters ofdistributed RFID tags according to an embodiment.

FIG. 2 is a schematic diagram showing use of bridge tags to implementcommunication between clusters according to an embodiment.

FIGS. 3-4 are schematic diagrams showing formation of clusters based ondistances between RFID tags according to an embodiment.

FIG. 5 is a flowchart of an embodiment of a method for stochasticcommunication between RFID tags, such as the RFID tags shown in FIGS.1-3.

FIG. 6 is a block diagram of an embodiment of a system to provide directtag-to-tag communication between passive RFID tags of clusters.

FIG. 7 is a schematic diagram illustratively showing modulation of acarrier wave (CW) by an embodiment of the system of FIG. 6 for directtag-to-tag communication between passive RFID tags of clusters.

FIG. 8 is a table showing example power levels associated with directtag-to-tag communication between RFID tags of clusters.

FIG. 9 is a flowchart of an embodiment of a method that can beimplemented in the system of FIG. 6 for direct tag-to-tag communicationbetween passive RFID tags of clusters.

FIGS. 10-12 are schematic diagrams that show example implementations fordirect tag-to-tag communication between passive RFID tags of clusters.

FIG. 13 is a schematic diagram that shows an embodiment of an apparatuswith RFID reading capability that is usable for direct tag-to-tagcommunication between passive RFID tags of clusters.

DETAILED DESCRIPTION

In the following description, numerous specific details are given toprovide a thorough understanding of embodiments. One skilled in therelevant art will recognize, however, that the embodiments can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations associated with RFID tags and RFIDreaders, computer and/or telecommunications networks, and/or computingsystems are not shown or described in detail to avoid obscuring aspectsof the embodiments.

Unless the context requires otherwise, throughout the specification andclaims which follow, the word “comprise” and variations thereof, suchas, “comprises” and “comprising” are to be construed in an open,inclusive sense, that is as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment. Thus, the appearances of the phrases “in oneembodiment” or “in an embodiment” in various places throughout thisspecification are not necessarily all referring to the same embodiment.Furthermore, the particular features, structures, or characteristics maybe combined in any suitable manner in one or more embodiments.

The headings provided herein are for convenience only and do notinterpret the scope or meaning of the embodiments.

As an overview, data carriers (such as RFID tags) are formed intoclusters of data carriers. Each cluster has at least one bridge datacarrier that can communicate with a bridge data carrier of anothercluster, thereby allowing data carriers in each cluster to communicatedirectly or indirectly with each other using a stochastic communicationprotocol method.

The clusters can be formed dynamically based on various criteria, suchas the distance associated with candidate data carriers, such as adistance between a candidate data carrier and a centrally located datacarrier in a cluster. Moreover, the size, shape, number of datacarriers, etc. for each cluster can vary dynamically from one cluster toanother.

Another embodiment relates to a synchronization of formed coalitions ofclusters of distributed data carriers to sustain a collection of data ofinterest in a desired manner.

Embodiments further provide techniques for direct tag-to-tagcommunication between data carriers (such as passive RFID tags) in eachcluster and/or between clusters. Such embodiments allow such datacarriers to backscatter and modulate a carrier wave from a source,thereby using the backscattered and modulated carrier wave to conveydata to each other.

The stochastic communication protocol method of one embodiment includesthe following elements:

(a) forming stochastic coalitions of clusters from irregularly orotherwise randomly distributed RFID tags;

(b) identifying bridge tags for each cluster;

(c) synchronizing cluster formations; and

(d) enabling distribution of information between RFID tags and a datacollection device.

FIG. 1 shows a non-limiting example of the first element (a) of such amethod, namely formation of stochastic coalitions of clusters fromdistributed RFID tags. In particular, the diagram of FIG. 1 showsformation of a plurality of clusters of data carriers, such as a set ofRFID tags Y={y₁, y₂, y₃, . . . , y_(N)}, according to one embodiment.For the sake of simplicity of explanation hereinafter and unlessotherwise specified, the data carriers will be described in the contextof RFID tags. In other embodiments, it is appreciated that the datacarriers can comprise acoustical tags, other types of non-RFID tags,and/or a combination of RFID tags and non-RFID tags.

Each of the clusters in FIG. 1 are denoted by C^(i), where 1≦i<k andk<N. Each cluster C includes an RFID tag x_(i), where 1≦i≦k. In oneembodiment, the RFID tag x_(i) in each cluster C^(i) comprises an RFIDtag that is located substantially in the center of each cluster. Thus,the cluster C¹ has the central RFID tag x₁; the cluster C² has thecentral RFID tag x₂; the cluster C³ has the central RFID tag x₃; and soforth up to the cluster C^(k) having the central RFID tag x_(k). Inanother embodiments, the RFID tag x_(i) need not necessarily be thecentrally located RFID tag in each cluster C^(i).

The various RFID tags Y in FIG. 1 include deployed RFID tags that areaffixed to objects. Such objects can include an item, a packaging orlabel for the item, a container of multiple packaged or unpackageditems, or other type of objects that are capable of having the RFID tagsY attached thereon. Examples of the item can include drugs, toys, food,animals, merchandise, human beings, machinery parts, or other types ofanimate or inanimate items that can be identified or otherwiserepresented by the RFID tags Y. In the context of human beings, forexample, the item can include an identification card, driver's license,airline boarding pass, article of clothing, luggage, and so forth.Moreover, the RFID tags Y can be affixed to stationary objects, such asobjects placed on an inventory shelf. The RFID tags Y may also beaffixed to objects in motion, such as on identification cards carried bypersons. The RFID tags may also be affixed to a combination ofstationary and in-motion objects, and may further dynamically change intotal number N (as well as the total number of RFID tags in each clusterC^(k)) as RFID tags are added or removed from a cluster, run out ofpower or are otherwise disabled, lost or detached from their respectiveobject, and so forth.

Accordingly in one embodiment, the RFID tags Y in FIG. 1 are randomlydistributed in a non-confined area. In another embodiment, thedistribution may be less random, for example if the objects having theRFID tags Y affixed thereon are organized uniformly on a shelf or othersituation where the distribution of the RFID tags Y is more or lessuniform.

The clusters C of FIG. 1 are formed based on the principles of coalitionformation in one embodiment. The coalitions (or other form of grouping)of the RFID tags Y of one embodiment define RFID tags as agents that mayor may not communicate with each other. Coalitions can be formed betweenlinked agents—thus, a coalition can encompass two (or more) clustersthat are able to communicate with each other; a coalition can encompasstwo (or more) RFID tags in different clusters that can communicate witheach other; and/or a coalition can encompass two (or more) RFID tags ina same cluster that can communicate with each other. In a first type ofcommunication in an embodiment, RFID tags directly communicate with eachother in order to be in the same coalition. In a second type ofcommunication in an embodiment, RFID tags may communicate indirectlywith each other through the use of other agents. In one embodiment, thestructure of the random coalitions controls the functionality of thecoalitions, and the efficiency of communication protocols between RFIDtags in effect determines the functionality of the coalitions. Furtherdetails of such various embodiments are described in further detaillater below. The publication Kirman et al., “Stochastic Communicationand Coalition Formation,” Econometrica, volume 54, No. 1 (January 1986),pages 129-138 also provides additional details of coalitions that can beimplemented by some embodiments and is incorporated by reference hereinin its entirety.

In mathematical terms for one embodiment, the set of RFID tags Y={y₁,y₂, y₃, . . . , y_(N)} is divided into k subsets (clusters C), with theRFID tags x_(i) being centrally located tags in each cluster, where1≦i≦k and k<N. Under these conditions, the following criterion will havea maximum value:

$\sum\limits_{x_{i}}^{\;}{\sum\limits_{y_{j} \in \;{S{(x_{i})}}}^{\;}{\mu\left( {x_{i},y_{j}} \right)}}$where S(x_(i)) is a set of RFID tags that belong to a cluster C^(i) withthe RFID tag x_(i) as a central RFID tag, and μ(x_(i),y_(j)) is somemeasure of communication quality between tags x_(i) and y_(j) (with iand j<N). In one embodiment, the measure of communication quality isbased on emitted power, as will be explained with regards to FIG. 2. Inother embodiments, the measure of communication quality can be based onadditional or alternative factors.

FIG. 2 shows a non-limiting example of the second element (b) of anembodiment of the stochastic communication protocol method, namelyidentification of bridge RFID tags for each cluster C^(i). In anembodiment, the identification of bridge RFID tags (e.g., the RFID tagsx_(p), y_(k), y_(i), and x_(i) in FIG. 2) includes identification ofRFID tags in every cluster C such that all clusters have links with eachother directly or indirectly through intermediate clusters via use ofbridge RFID tags.

In the example of FIG. 2, the cluster 1 includes a particular RFID tagx_(p). The RFID tag x_(p) may be the central RFID tag or may be someother tag located off-center in the cluster 1. The cluster 2 includesparticular RFID tags y_(k) and y_(j). The RFID tags y_(k) or y_(j) maybe the central RFID tag or may be some other tag located off-center inthe cluster 2. The cluster 2 also includes other RFID tags y_(a) andy_(b) that can communicate with each other, as depicted by thedouble-headed arrow between the RFID tags y_(a) and y_(b). The cluster 3includes the RFID tag x_(i). The RFID tag x_(i) may be the central RFIDtag or may be some other tag located off-center in the cluster 3.

In the example of FIG. 2, the RFID tags x_(p) and y_(k) are the bridgeRFID tags that can communicate with each other (as depicted by thedouble headed arrow between the RFID tags x_(p) and y_(k)), therebyallowing other RFID tags in the respective clusters 1 and 2 toindirectly communicating with each other through the bridge RFID tagsx_(p) and y_(k). Thus, a coalition is formed between the bridge RFIDtags x_(p) and y_(k), between the clusters 1 and 2, and/or between anyRFID tag in cluster 1 with any RFID tag in cluster 1 (via communicationwith the bridge RFID tags x_(p) and y_(k)).

Similarly, the RFID tags y_(j) and x_(i) are the bridge RFID tags thatcan communicate with each other (as depicted by the double headed arrowbetween the RFID tags y_(j) and x_(i)), thereby allowing other RFID tagsin the respective clusters 2 and 3 to indirectly communicating with eachother through the bridge RFID tags y_(j) and x_(i). Thus, a coalition isformed between the bridge RFID tags y_(j) and x_(i), between theclusters 2 and 3, and/or between any RFID tag in cluster 2 with any RFIDtag in cluster 3 (via communication with the bridge RFID tags y_(j) andx_(i)).

In an embodiment, a “bridge zone” in each cluster (e.g., in clusters 1and 2) is defined by the region where the emitting power of theparticular RFID tag x_(p) of the cluster 1 that is sensed by theparticular RFID tag y_(k) of the cluster 2 exceeds a cumulative powerthat is sensed by the particular RFID tag y_(k) from all of the RFIDtags in the cluster 1 by some specified threshold value. In someembodiments, the specified threshold value exceeded by the cumulativepower is uniform among the various clusters. In another embodiment, thespecified threshold value can be different among the various clusters.For instance, the specified threshold value between clusters 1 and 2 canbe different than the specified threshold value between clusters 2 and3.

In an embodiment, a single cluster may have different bridge RFID tagsthat can be used to bridge with respective different other clusters.Further in an embodiment, a single cluster may have more than one bridgeRFID tag to bridge with some other single cluster, and/or may bridgewith more than one bridge RFID tag of that other single clusters. Stillfurther in an embodiment, various RFID tags may be designated as backupbridge RFID tags, if a primary bridge RFID tag becomes disabled, isremoved from the cluster, or otherwise becomes incapable of operating asa bridge RFID tag.

In yet further embodiments, the identification of bridge RFID tags maychange dynamically, as the shape or size of a cluster changes and/or asadditional RFID tags are added/removed from the cluster. It is thereforeevident from the above that individual RFID tags are capable ofcommunicating with other RFID tags, whether in the same cluster or insome other cluster, by “hopping” from one RFID tag to anothercommunicatively compatible RFID tag in the same cluster and betweenclusters.

FIGS. 3-4 show an embodiment of a technique for forming clusters basedon distances between RFID tags. It is appreciated that formation ofclusters based on distances is only one possible technique that can beused. Other embodiments can form clusters based on other alternative oradditional factors, such as RFID type, power output, return signalfrequency, and so forth.

In FIG. 3, a plurality of RFID tags 300 are distributed over a region.The region over which the RFID tags 300 are distributed can range from afew square inches (or smaller) to perhaps on the order of several squaremiles. As depicted symbolically in FIG. 3, some RFID tags 300 arelocated in closer proximity relative to each other as compared to otherones of the RFID tags 300. The particular concentration/density,pattern, location, or other distribution factor of the RFID tags 300 canbe completely random, semi-random, specifically arranged, and/orcombination thereof.

As depicted in FIG. 4, clusters 400 of the RFID tags 300 are formedbased on distances between RFID tags 300. Specifically in oneembodiment, RFID tags 300 that are closer in distance to each other areformed into the same cluster. Various techniques can be used todetermine whether the distance between RFID tags is sufficient orinsufficient to justify inclusion of any given RFID tag into a cluster.In one technique, RFID tags are included in the same cluster if thedistance between any two of the RFID tags is less than some specifieddistance. Any RFID tag that exceeds the specified distance to theclosest RFID tag of the cluster is rejected for inclusion in thecluster, and is considered instead for inclusion in some other cluster.

In another technique, a particular RFID tag is designated as a centralRFID tag x_(i) for a cluster. Then, the other RFID tags of the clusterare identified and selected based on some specified distance from thecentral tag x_(i). For example, RFID tags are included in the samecluster if the distance between such RFID tags and the central RFID tagx_(i) is less than some specified distance. Any RFID tag that exceedsthe specified distance to the central RFID tag x_(i) of the cluster isrejected for inclusion in the cluster, and is considered instead forinclusion in some other cluster.

Again and as previously explained above, the size, shape, number of RFIDtags, etc. of each cluster can dynamically vary from one cluster toanother based on various factors. Moreover, it is possible to have acluster having only a single RFID tag. Such single RFID tag can thus actas its own bridge RFID tag to other clusters.

In an embodiment, each of the clusters previously described aboveincludes at least one active RFID tag and one or more passive RFID tags.In another embodiment, all RFID tags in one or more of the clusters maybe passive RFID tags, and one or more devices (such as an automatic datacollection device, including RFID readers) can provide the RF field(s)to power such passive RFID tags to perform the various functionalitiesdescribed herein. In yet other embodiments, some clusters may have oneactive RFID tag and one or more passive RFID tags, while other clustersmay have only passive RFID tags, while still other clusters may haveonly active RFID tags—all of these clusters have the capability tocommunicate with each other (directly or indirectly) using the methodsdescribed herein.

FIG. 5 is a flowchart of an embodiment of a method 500 to implement thevarious elements of the stochastic communication protocol describedabove. It is appreciated that the various operations in the flowchart ofFIG. 5 need not necessarily occur in the exact order shown. Moreover,certain operations can be added, removed, modified, or combined.

In some embodiments, certain operations of the method 500 can beimplemented in software or other machine-readable instruction stored ona machine-readable medium and executable by a processor. For example,some of the operations in the method 500 can be performed by a datacollection device (such as an RFID reader) in one embodiment, using oneor more processors and a storage medium of the data collection device.

At a block 502, all of the RFID tags are assigned to a particularcluster that has some RFID tag x_(i) as a central tag, thereby formingclusters of RFID tags. As described above with reference to FIGS. 3-4,the assignment of tags to a particular cluster can be based on distancesbetween RFID tags. Also as explained above, other criteria can be usedto assign RFID tags to specific clusters.

At a block 504, bridge RFID tags are identified and selected. Asdescribed above for one embodiment, the identification and selection ofbridge RFID tags can be performed based on bridge zones where theemitting power of the particular RFID tag of a first cluster that issensed by a particular RFID tag of a second cluster exceeds somecumulative power of all RFID tags of the first cluster that is sensed bythe particular RFID tag of the second cluster.

At a block 506 for one embodiment, communication between and/or withinclusters is synchronized, such as time synchronization of transmissionand/or reception. The synchronization can be localized (e.g.,synchronization between neighboring RFID tags in a same and/or adjacentclusters) and/or at least partially global (e.g., synchronizationbetween all RFID tags in a same cluster, synchronization between aplurality of clusters, synchronization of all RFID tags of allclusters). In one embodiment, such synchronization can be performedusing methods known to persons skilled in the art. Other embodiments canuse the synchronization techniques disclosed in U.S. Provisional PatentApplication Ser. No. 60/610,759, entitled “SYNCHRONIZATION OF ADAPTIVESELF-CONFIGURING WIRELESS NETWORK OF TRANSPONDERS,” filed Dec. 1, 2004,assigned to the same assignee as the present application, andincorporated herein by reference in its entirety.

One example of such synchronization techniques includes global-basedtime synchronization in which all RFID tags set time to send/receivedata based on a single (e.g., a common) time clock located inside and/oroutside of the RFID network. In one embodiment that can implement thissynchronization technique, an RFID tag is able to receive data eventhough such an RFID tag may not necessarily have the capability tocommunicate the acknowledgement of a successful reception of the data,due to factors such as power constraints. This synchronization techniqueis used for global synchronization in one embodiment, but can also beadapted for local synchronization.

Another example is time-stamped packet communication in which thepackets or other data format received by a recipient RFID tag includes atime of transmission from a sender RFID tag. Embodiments can implementthis synchronization technique in a global and/or localized basis.

Yet another example is tag-to-tag synchronization in which the time fortransmission/reception is set by an outside system and propagated to theRFID tags. Such propagation can be done by having the RFID tags withinand/between clusters send the time from one RFID tag to another.

A variation to the tag-to-tag synchronization involves an RFID tag(performing managerial duties for its cluster) that sets the time andpropagates the time to collaborating neighbor RFID tags. In oneembodiment, the central RFID tag x_(i) can be used as the managerialtag, although other RFID tags in the cluster may also be used as primaryand/or backup managerial RFID tags. The cluster's time may besynchronized locally or globally when a tag-to-tag synchronizationtechnique is used.

Still another example of synchronization involves multi-hop timesynchronization in which time error is compensated/corrected duringpropagation of data. In still a further example, RFID tags are capableof identifying a synchronization mode and can start corroboration withneighboring RFID tags in accordance with a proposed synchronizationmode. Furthermore, in the case of multiple clusters of RFID tags, RFIDtags may reconcile multiple global times to continue an appropriatecommunication mode.

In other embodiments, the synchronization at the block 506 need not beperformed and/or need be performed only on a limited basis. Thus forsuch embodiments, there need not necessarily be synchronization betweenRFID tags in a same cluster, between RFID tags of different clusters,between clusters, and/or between other communicating elements of theRFID networks.

At a block 508 in the method 500 of FIG. 5, information is communicatedbetween RFID tags, clusters, and/or data collection device(s) or otherdevice(s). Such communication can be direct or indirect communicationwithin or between clusters using the bridge RFID tags as describedabove. Specific embodiments of direct tag-to-tag communication that canbe implemented in the clusters previously described above will beexplained next.

More particularly and beginning with FIG. 6, shown generally at 600 isan embodiment of a system 600 for direct tag-to-tag communicationbetween two passive RFID tags 1 and 2. The RFID tags 1 and 2 cancomprise two bridge RFID tags of two different clusters described above,or two RFID tags within the same cluster, for instance. Either or bothRFID tags 1 and 2 can in turn perform direct tag-to-tag communicationwith yet other RFID tags in the same cluster and/or with a bridge RFIDtag, thereby allowing indirect communication with yet other RFID tags inanother cluster.

For embodiments of the system 100 having RFID tags, the system 600includes an RF carrier wave (RF CW) source 602 that generates a carrierwave 604. The RF CW source 602 can be embodied as an automatic datacollection device (such as an RFID reader), a cellular telephone orother portable communication device, another RFID tag, and or any otherdevice(s) or combination thereof that are capable of generating anunmodulated carrier wave 604 that can be used for direct tag-to-tagcommunication, as well as a power source for the RFID tags 1 and 2. Inanother embodiment, the carrier wave 604 is output from the RF CW source602 in a modulated form, and is then further modulated by the RFID tags1 and 2 during tag-to-tag communication.

In one embodiment, the RF CW source 602 can be switched ON or OFFmechanically (such as by an operator) or electronically (such as inresponse to a wireless signal). The RF CW source 602 can be powered froma portable battery, thereby providing a portable solution, or from astationary source of power, for example a 120 V AC voltage supply,thereby providing an industrial solution. Moreover, the RF CW source 602can be integrated as an operating mode option in a cellular telephone orother device, and produced inexpensively since no frequency stability ordigital signal processing capability is used in one embodiment.

An example embodiment of the RF CW source 602 can use a 5 V battery withup to 1 watt of output RF power, using Micro Device's RF2131 poweramplifier integrated circuit (IC) with resonant feedback. Additionallyin an embodiment, several RC CW sources 602 can be arranged in an arrayor other pattern so as to cover a large area where clusters of RFID tagsare present.

In operation the carrier wave 604 is backscattered, and the RFID tags 1and 2 can communicate with each other by modulating the backscatteredcarrier wave 604. Thus, the RFID tag 1 can send an interrogation signal606 to the RFID tag 2, and the RFID tag 2 can reply to the interrogationsignal 606 with a reply signal 608, and/or vice versa. The interrogationsignal 606 and the return signal 608 are thus the modulatedbackscattered carrier wave 604. The interrogation signal 606 and thereturn signal 608 can be demodulated by the RFID tags 2 and 1,respectively, to obtain the data encoded therein.

The method of communication of FIG. 6 can be analogized by an example oftwo persons in a dark room. When a light in the room if OFF, the twopersons cannot see each other in the dark. When the light in the room isON, the two persons can see each other and remember each other'sappearance because of photons of light that reflect from them and makethem visible to each other. In an analogous way, the two passive RFIDtags 1 and 2 cannot communicate with each other in the absence of thecarrier wave 604, but in the presence of the carrier wave 604, the twoRFID tags 1 and 2 can communicate with each other by modulating thebackscattered carrier wave 604.

Example waveforms at terminals of the RFID tags 1 and 2 duringtag-to-tag communication are illustrated in FIG. 7. It is appreciatedthat such illustrated waveforms are not intended to be preciselydepicted in shape, frequency, amplitude, timing, etc. in FIG. 7, but arerather intended to be drawn for the purpose of clarity of explanation.

The carrier wave 604 is depicted in FIG. 7 as a signal of constantamplitude during periods of time when the carrier wave 604 is not beingmodulated by the RFID tags 1 and 2. During a period of time when theRFID tag 1 generates and sends the interrogation signal 606 to the RFIDtag 2, FIG. 7 depicts the modulation of the carrier wave 604 as a squarewave pulse train. Similarly, during a period of time when the RFID tag 2generates and sends the return signal 608 to the RFID tag 1, FIG. 7depicts the modulation of the carrier wave 604 as another square wavepulse train.

FIG. 8 is a table 800 showing example power budget values for thetag-to-tag communication described above. It is appreciated that thevarious power values shown in the table 800 are merely for the purposeof illustration, and that other embodiments may involve different powervalues.

The RF CW source 602 is assumed to output the carrier wave 604 with apower value of +36 dBm. The free space path loss from the RF CW source602 to the RFID tag 1 (assuming a distance of 4 feet between the RF CWsource 602 and the RFID tag 1, with a 915 MHz frequency for the carrierwave 604) is −33 dB, thereby leaving +3 dBm of power available. There isthen a backscattering modulation loss of −6 dB associated with the RFIDtag 1, as well as a coupling loss of −6 dB between the RFID tags 1 and 2in close proximity. The resulting backscattering differential modulatedpower received by the RFID tag 2 is thus −9 dBm. If the minimum powerrequired for tag-to-tag communication is −10 dBm, then the resultant −9dBm power is sufficient to meet operational requirements.

In one embodiment, the carrier wave 604 from the RF CW source 602comprises an interrogation signal that both powers and interrogates theRFID tag 1 and/or the RFID tag 2. Such an interrogation signal can thenbe modulated by the RFID tag 1 and/or the RFID tag 2 in the mannerdescribed above, thereby providing tag-to-tag communication capabilitiesin existing passive RFID networks/systems.

In another embodiment, one of the RFID tags (such as the RFID tag 2) cancomprise a passive RFID tag with capabilities to receive interrogationsignals and to send return signals, and another one of the RFID tags(such as the RFID tag 1) can comprise a passive RFID tag havingadditional capability to independently broadcast or otherwise issue tagqueries (i.e., interrogation signals), alternatively or additionally tousing the carrier wave 604 for such tag queries. Such an embodiment ofthe RFID tag 1 obtains power from the carrier wave 604 (or from someother source) and then waits for the RF CW source 602 to transmit aninterrogation signal, which may be in the form of a modulation of thecarrier wave 604 and/or the issuance of another signal. If the RFID tag1 does not receive any interrogation signals from the RF CW source 1within a period of time, then the RFID tag 1 starts to periodicallybroadcast (such as by backscattering) interrogation signals itself tothe RFID tag 2 and/or to other RFID tags. Such interrogation signals cancomprise a modulated or unmodulated carrier wave similar to the carrierwave 604, in one embodiment.

In another embodiment, both the RFID tags 1 and 2 can have thecapability to issue interrogation signals. In still further embodiments,RFID tags of the various clusters can comprise a mix of RFID tags withor without this additional capability to issue interrogation signals.

FIG. 9 is a flowchart of a method 900 for direct tag-to-tagcommunication in which one of the RFID tags (such as the RFID tag 1 forpurposes of illustration) has capability to issue interrogation signals.It is appreciated that the various operations in the flowchart of FIG. 9need not necessarily occur in the exact order shown. Moreover, certainoperations can be added, removed, modified, or combined.

In some embodiments, certain operations of the method 900 can beimplemented in software or other machine-readable instruction stored ona machine-readable medium and executable by a processor. For example,some of the operations in the method 900 can be performed by one or morecontrollers or other processor(s) and a storage medium in an RFID tag.

At a block 902, the RFID tags 1 and 2 receive the carrier wave 604 fromthe RF CW source 602 and power up. A timer in the RFID tag 1 is startedat a block 904. If the RFID tag 1 receives an interrogation signal at ablock 906 from the RF CW source 602 and/or from some other queryingdevice, then the RFID tag 908 operates in a normal tag mode at a block908, such as by generating and sending an appropriate return signal tothe querying device(s).

However, if the timer expires at a block 910 and the RFID tag 1 has notreceived an interrogation signal at the block 906, then the RFID tag 1sends one or more interrogation signals or other types of queries at ablock 912 to an RFID tag (such as the RFID tag 2). In one embodiment,the queries at the block 912 are broadcast periodically, such as bybackscattering. In other embodiments, the queries need not necessarilybe sent in a periodical manner, and can be sent in a somewhat randommanner, for example.

If the RFID tag 1 does not receive any return signals or otherresponse(s) to the queries at a block 914, then the RFID tag 1 continuesto issue queries at the block 912. However, if the RFID tag 1 receivesone or more responses at the block 914, then the RFID tag 1 generatesand sends back (such as by backscattering) a corresponding one or moreacknowledgements at a block 916.

At a block 918, the RFID tag 1 receives an RFID tag identifier (such asthe identifier for the RFID tag 2) from the RFID tag 2 during the directtag-to-tag communication and stores this received RFID tag identifier inmemory. The method 900 then repeats at the block 904 in which the timerof the RFID tag 1 is restarted as the RFID tag 1 monitors for additionaltag queries.

FIGS. 10-12 show various example implementations for direct tag-to-tagcommunication where RFID tags (or other types of data carriers, such asacoustical tags) are arranged in clusters. It is appreciated that suchimplementations are not intended to be exhaustive of all the possibleimplementations for direct tag-to-tag communication.

The implementation illustrated in FIG. 10 involves direct exchange ofinformation, without the use of a dedicated automatic data collectiondevice such as an RFID reader, between documents embedded with passiveRFID tags containing information pertaining to the documents. Examplesof such documents as illustrated in FIG. 10 are business cards 1000 and1002, such that the passive RFID tags embedded therein contain businesscard information.

The exchange of business card information can be performed if there isan area 1004 where the carrier wave 604 is present to energize the RFIDtags embedded in the business cards 1000 and 1002. The area 1004 can bean area in a conference center, for example, is covered by the carrierwave 604 generated by the RF CW source 602. Alternatively oradditionally, the carrier wave 604 can be generated from a device suchas a cellular telephone 1006 or other device capable to generate thecarrier wave 604. In one embodiment, the cellular telephone 1006 can bea conventional cellular telephone that does not require modification inorder to generate the carrier wave 604.

FIG. 11 further illustrates the implementation shown in FIG. 10. Twopersons need to quickly and conveniently exchange business cardinformation. One of these persons pushes a button on the cellulartelephone 1006 to create a “bubble” or other area proximate to thebusiness cards 1000 and 1002 to be covered by the carrier wave 604. Bypressing the button or otherwise appropriately actuating the cellulartelephone 1006, the cellular telephone 10056 can operate in an RF CWmode. The “bubble” can be present for a few seconds or any othersuitable length of time sufficient to allow the RFID tags of thebusiness cards 1000 and 1002 to conduct tag-to-tag communication.

The two persons can “rub” their business cards 1000 and 1002 together,or otherwise place the business cards 1000 and 100 in close proximity toeach other, in order to conduct the tag-to-tag communication to exchangeand store business card information of the other person. The two personscan then go their separate ways, and can later retrieve the storedbusiness card information (such as at home, at the office, or at someother location). The business card information stored in the embeddedRFID tag of the business cards 1000 and 1002 can be retrieved at suchother locations using an automatic data collection device (such as anRFID reader), a personal computer of laptop with RFID-readingcapability, or other device capable to read RFID tags.

In the example of FIG. 12, a person approaches a bulletin board 1200having advertisements 1202 present thereon. The advertisements 1202 havepassive RFID tags that contain information pertaining to eachadvertisement 1202. An area 1204 (“bubble”) encompassing the bulletinboard 1200 is covered by the carrier wave 604 from the RF CW source 602,which could be a stationary device placed proximate to the bulletinboard 1200, a cellular telephone of the person, or some other device.

The person can read the information from selected advertisements 1202using a personal passive RFID tag 1206, such as by “swiping” the RFIDtag 1206 over the selected advertisement(s) 1202. The information readfrom the RFID tags of the advertisements 1202 can then be stored by theRFID tag 1206 of the person for later review or other use.

In an embodiment, the RFID tag 1206 of the user can be embedded in abusiness card or other object, in a handheld device portablecommunication device (such as a cellular telephone, pager, PDA,Blackberry, Palm Pilot, etc.), or some other compact and portableapparatus that can be conveniently carried by the person and usable to“swipe” over one or more RFID tags or other target data carriers.

An embodiment of such an apparatus having the RFID tag for reading otherRFID tags is shown at 1300 in FIG. 13. The apparatus 1300 can be a“paper thin” batteryless RFID reader, with an example thickness of 0.1mm. The apparatus 1300 of one embodiment comprises a passive RFID taghaving capability to issue interrogation or other query signals inaccordance with the embodiment of the method 900 shown in FIG. 9. Theapparatus 1300 of one embodiment can be provided with sufficient memorycapacity to store information from a large number of RFID tags that areread. The stored information can later be retrieved from the apparatus1300 using an RFID reader or other suitable automatic data collectiondevice.

Advantages of the apparatus 1300 are compact size, lightweight,batteryless, and relatively inexpensive (for example, less than a fewdollars each). Moreover, such an apparatus 1300 can operate anywhere ina vicinity of RFID tags that are covered by the carrier wave 604generated by the RF CW source 602.

Accordingly from the various embodiments of the RFID clusters andtag-to-tag communication techniques between RFID tags of such clustersdescribed above, it is clear that such embodiments can be used for realtime applications and/or to meet other application requirements.Additional advantages of such embodiments can further include, but notbe limited to, indifference to RFID network topology changes (e.g.,adaptive and self-configuring clusters), energy efficient functionality,extended range for automatic data collection device or other device forcollecting data (since tags can communicate directly or indirectly witheach other using bridge tags), thereby extending the range for readingtags), self-organizing capability, and so forth.

All of the above U.S. patents, U.S. patent application publications,U.S. patent applications, foreign patents, foreign patent applicationsand non-patent publications referred to in this specification and/orlisted in the Application Data Sheet, are incorporated herein byreference, in their entirety.

The above description of illustrated embodiments, including what isdescribed in the Abstract, is not intended to be exhaustive or to limitthe invention to the precise forms disclosed. While specific embodimentsand examples are described herein for illustrative purposes, variousequivalent modifications are possible within the scope of the inventionand can be made without deviating from the spirit and scope of theinvention.

For example, embodiments have been described above in which the RFIDtags are attached to objects, and provide data pertaining to theobjects. In other embodiments, the RFID tags may be provided with sensorelements, such that the RFID tags can detect and collect data regardingtemperature, humidity, air pressure, lighting levels, presence ofcertain chemical substances, presence and strength of electromagnetic orother types of signals, or other environmental condition that can besensed and stored by the RFID tags. Such detected and collected data canthen be provided to one or more RFID readers and/or to other RFID tagsusing the techniques described above.

Furthermore, various embodiments have been described above in thecontext of the data carrier being in the form of an RFID tag. It isappreciated that other embodiments can be provided for use with othertypes of data carriers, such as acoustical tags. In such otherembodiments, the carrier wave (CW) can be in the form of an acousticalwave. Further in such embodiments, the acoustical tags can be formedinto clusters and can communicate with each other in a manner analogousto the techniques described above. Further, various systems can includeclusters formed entirely of acoustical tags; clusters formed from a mixof acoustical tags, RFID tags, and/or other types of tags; and/orclusters formed from various other combinations of tag types that cancommunicate with similarly or differently formed clusters.

In the embodiments described above, various signals (such as the carrierwave 604) have been described as being an RF signal. It is understoodthat the RF signal(s) can be included in at least the radio band andmicrowave band of frequencies.

These and other modifications can be made to the embodiments in light ofthe above detailed description. The terms used in the following claimsshould not be construed to limit the invention to the specificembodiments disclosed in the specification and the claims. Rather, thescope of the invention is to be determined entirely by the followingclaims, which are to be construed in accordance with establisheddoctrines of claim interpretation.

1. A method, comprising: forming clusters of distributed data carriers;for each of said clusters, identifying a bridge data carrier that isoperable to communicate with a bridge data carrier of another of saidclusters by defining a bridge zone as a region where a power outputlevel from said at least one of said data carriers in a first cluster,which is sensed by another one of said data carriers in a secondcluster, exceeds a cumulative power that is sensed by said another oneof said data carriers from all of the data carriers in the first clusterby a threshold value; enabling communication between data carriers ofthe different clusters via the identified bridge data carrier, at leastsome of said data carriers including batteryless passive data carriers,wherein each data carrier in the cluster is operable to communicate withthe respective bridge data carrier; and forming coalitions of clustersof distributed data carriers based on the enabled communication betweenthe data carriers of the different clusters, each coalition of clustersincluding at least two of the clusters of distributed data carriers. 2.The method of claim 1 wherein at least some of said batteryless passivedata carriers include passive RFID tags.
 3. The method of claim 1wherein at least some of said batteryless passive data carriers includesacoustical tags.
 4. The method of claim 1 wherein forming coalitions ofclusters of distributed data carriers includes forming coalitions ofrandomly distributed data carriers, said coalitions including acoalition between clusters, a coalition between data carriers ofrespective different clusters, and a coalition between data carriers ina same cluster.
 5. The method of claim 1 wherein forming coalitions ofdistributed data carriers includes identifying candidate data carriersto place in a cluster based on whether a distance between said candidatedata carriers is within a value.
 6. The method of claim 5 wherein one ofsaid identified candidate data carriers is a substantially central datacarrier, wherein said distance is a distance between the central datacarrier and another of said candidate data carriers.
 7. The method ofclaim 1 wherein enabling the communication between the data carriersincludes enabling indirect communication between non-bridge datacarriers of different clusters using their respective bridge datacarriers, enabling direct or indirect communication between datacarriers in a same cluster, or enabling communication between datacarriers of different clusters using their respective bridge datacarriers and at least one intermediate cluster and the bridge datacarriers of the intermediate cluster.
 8. The method of claim 1 whereinenabling communications between data carriers of the clusters includes:providing a carrier wave that can be backscattered; modulating thebackscattered carrier wave with a first of said data carriers togenerate an interrogation signal; and modulating the backscatteredcarrier wave with a second of said data carriers to generate a returnsignal in response to the interrogation signal.
 9. The method of claim 8wherein the first of said data carrier initiates modulation of thebackscattered carrier wave by: receiving power from the carrier wave;and monitoring for a query signal associated with the carrier wave for aperiod of time; wherein when the query signal is not detected afterexpiration of the period of time, generating and sending theinterrogation signal to query the second of said data carriers; and whenthe query signal is detected prior to expiration of the period of time,responding to the query signal.
 10. The method of claim 8 whereinproviding the carrier wave includes providing the carrier wave from aportable data collection or communication device.
 11. The method ofclaim 8 wherein providing the carrier wave includes providing thecarrier wave from another data carrier that is adapted to generate thecarrier wave.
 12. The method of claim 11 wherein said another datacarrier is embedded in a business card, an advertisement, or a document.13. The method of claim 1 wherein forming coalitions of clusters ofdistributed data carriers includes forming a cluster having only onedata carrier.
 14. The method of claim 1 wherein forming coalitions ofclusters of distributed data carriers includes forming coalitions havinga mix of battery powered active data carriers and said passive datacarriers.
 15. The method of claim 1 wherein enabling communicationbetween data carriers of the clusters includes enabling communicationusing a stochastic communication protocol that includes synchronizationof communication.
 16. The method of claim 15 wherein the synchronizationof communication includes localized time synchronization between atleast two data carriers.
 17. The method of claim 15 wherein thesynchronization of communication includes global time synchronizationbetween data carriers of a plurality of said clusters.
 18. The method ofclaim 15 wherein the synchronization of communication includesglobal-based time synchronization in which communication time betweendata carriers is set in accordance with a common time clock.
 19. Themethod of claim 15 wherein the synchronization of communication includestime-stamped data communication in which data received by a recipientdata carrier from a sender data carrier includes a time of transmissionof the data.
 20. The method of claim 15 wherein the synchronization ofcommunication includes data carrier-to-data carrier synchronizationincludes: setting a time, and propagating the set time from one datacarrier to another; or using one of the data carriers designated as amanagerial data carrier to set the time, and propagating the set timefrom the managerial data carrier to neighbor data carriers.
 21. Themethod of claim 15 wherein the synchronization of communication includesmultiple-hop time synchronization in which time error is compensated forduring communication.
 22. The method of claim 15 wherein thesynchronization of communication includes: providing a plurality ofdifferent synchronization modes; and allowing at least some of the datacarriers to identify one of said synchronization modes and tocorroborate with neighbor data carriers in accordance with theidentified synchronization mode.
 23. A system, comprising: At least afirst and second clusters of distributed data carriers, wherein for eachof said first and second clusters, a bridge data carrier is identifiedthat is operable to link with a bridge data carrier of another of saidfirst and second clusters; and means for enabling communication betweenthe data carriers of the first and second clusters, some of said datacarriers including batteryless passive carriers, wherein said bridgedata carrier is identified according to a region where a power outputlevel from a first data carrier in the first cluster, which is sensed bya second data carrier in the second cluster, exceeds a cumulative powerthat is sensed by said second data carrier from all of the data carriersin the first cluster by a threshold value.
 24. The system of claim 23wherein said means for enabling communication between data carriers ofthe clusters includes: source means for providing a carrier wave thatcan be backscattered; and means for modulating the backscattered carrierwave to generate interrogation and return signals therefrom, saidinterrogation and return signals being communicated between at least twoof said data carriers.
 25. The system of claim 24 wherein one of saiddata carriers includes means for independently generating theinterrogation signal after an expiration of time, alternatively oradditionally to generating the interrogation signal using the carrierwave.
 26. The system of claim 23 wherein said clusters includes acandidate data carrier placed in a particular cluster based on adistance between said candidate data carrier and a substantially centraldata carrier in the particular cluster.
 27. A system, comprising: aplurality of clusters of distributed data carriers, some of said datacarriers including batteryless passive data carriers; and for each ofsaid clusters, a bridge data carrier that is operable to link with abridge data carrier of another of said clusters to enable communicationbetween data carriers of the clusters, said communication includingmodulation of a backscattered carrier wave to convey interrogation andreturn signals between data carriers of the clusters, wherein themodulation of the backscattered carrier wave is initiated by: receivingpower from the carrier wave; and monitoring for a query signalassociated with the carrier wave for a period of time, wherein when thequery signal is not detected after expiration of the period of time,generating and sending the interrogation signal to query the second ofsaid data carriers; and when the query signal is detected prior toexpiration of the period of time, responding to the query signal, andwherein the bridge data carriers are determined based at least in parton a region where a power output level from a first data carrier in afirst cluster, which is sensed by a second data carrier in a secondcluster, exceeds a cumulative power that is sensed by said second datacarrier from all of the data carriers in the first cluster by athreshold value.
 28. The system of claim 27, further comprising acarrier wave source to generate the carrier wave.
 29. The system ofclaim 28 wherein said carrier wave source includes portable wirelesscommunication device, one of said data carriers embedded in an object,or an automatic data collection device.
 30. The system of claim 28wherein said one of said data carriers embedded in the object is adaptedto generate the carrier wave to interrogate at least another one of saiddata carriers in response to expiration of a specified time period. 31.The system of claim 27 wherein said clusters include dynamically formedclusters of randomly distributed data carriers that can communicate witheach other using a stochastic communication protocol.
 32. The system ofclaim 27 wherein each of the clusters includes a substantially centraldata carrier, wherein a candidate data carrier is adapted to beconsidered to include in a particular cluster based on a distancebetween the candidate data carrier and the central data carrier of theparticular cluster.
 33. An article of manufacture, comprising: a storagemedium usable with a plurality of distributed data carriers arrangedinto clusters, the storage medium having instructions stored thereonthat are executable by a processor associated with a first passive datacarrier to provide communication between passive ones of said datacarriers, by: receiving a carrier wave; starting a timer; monitoring foran interrogation signal; when the interrogation signal is not receivedbefore expiration of the timer, generating the interrogation signal bymodulating the carrier wave; sending the interrogation signal to atleast a second data carrier; and continuing to send the interrogationsignal to the second data carrier until a response signal is receivedfrom the second data carrier, wherein the storage medium furtherincludes instructions stored thereon that are executable by saidprocessor to provide communication between passive ones of said datacarriers, by identifying a bridge data carrier associated with thecluster of the second data carrier based at least in part on acumulative output power level of at least some of the data carriers inthe cluster of the second data carrier, wherein the bridge data carrieris identified based at least in part on a region where a power outputlevel from the bridge data carrier sensed by one of data carriers in thecluster of the first data carrier exceeds the cumulative power outputlevel of all the data carriers in the cluster of the second datacarrier, that is sensed by the one of the data carriers in the clusterof the first data carrier, by a threshold value.
 34. The article ofmanufacture of claim 33 wherein the second data carrier is in adifferent cluster than the first passive data carrier, said instructionsto send the interrogation signal including instructions that areexecutable by said processor to provide communication between passiveones of said data carriers, by: sending the interrogation signal to abridge data carrier associated with the cluster of the second datacarrier.
 35. The article of manufacture of claim 33 wherein the firstand second data carriers are both passive RFID data carriers of a sameor different cluster.
 36. The article of manufacture of claim 33 whereinsaid storage medium is at least partially integrated with a sensor. 37.The article of manufacture of claim 36 wherein said sensor is adapted todetect and collect data regarding at least one of a plurality ofparameters related to temperature, humidity, air pressure, lightinglevels, presence of certain chemical substances, presence and strengthof electromagnetic or other types of signals, or other environmentalcondition.
 38. The article of manufacture of claim 33 wherein the firstpassive data carrier is adapted to generate a broadcast signal.
 39. Thearticle of manufacture of claim 33 wherein the response signal of thesecond data carrier is a broadcast signal.